1. Field of the invention
The present invention relates to wireless communications, and more particularly, to an uplink reference signal transmission method for mitigating an interference in a multi-node system, and a user equipment using the method.
2. Related Art
A data transfer amount of a wireless network has been rapidly increased in recent years. It is because various devices, e.g., a smart phone, a tablet personal computer (PC), or the like, that require machine-to-machine (M2M) communication and a high data transfer amount have been introduced and distributed. To satisfy the required high data transfer amount, a carrier aggregation technique, a cognitive radio technique, or the like for effectively using more frequency bands and a multiple antenna technique, a multiple base station cooperation technique, or the like for increasing data capacity within a limited frequency have recently drawn attention.
In addition, the wireless network has been evolved in a direction of increasing density of nodes capable of accessing to an area around a user. Herein, the node implies an antenna (or antenna group) which is separated from a distributed antenna system (DAS) by more than a certain distance. However, the node is not limited to this definition, and thus can also be used in a broader sense. That is, the node may be a pico-cell evolved node B (PeNB), a home eNB (HeNB), a remote radio head (RRH), a remote radio unit (RRU), a relay, etc. A wireless communication system having nodes with higher density can provide higher system performance through cooperation between the nodes. That is, better system performance can be achieved when one base station controller manages transmission and reception of respective nodes and thus the nodes operate as if they are antennas or an antenna group for one cell, in comparison with a case where the respective nodes operate as an independent base station (BS), advanced BS (ABS), Node-B (NB), eNode-B (eNB), access point (AP), etc., and thus do not cooperate with each other. Hereinafter, a wireless communication system including a plurality of nodes is referred to as a multi-node system.
In the multi-node system, a plurality of nodes can use one physical cell identifier (ID). Accordingly, there is an advantage in that the number of handover attempts is decreased, and cooperative communication between the nodes becomes easy.
In the conventional technique, a user equipment (UE) generates various uplink signals on the basis of a physical cell ID used by a BS or a node. However, an interference between uplink signals is increased in proportion to the number of UEs in a cell. In particular, an interference between uplink reference signals may be problematic.